Heretofore, as a clinical thermometer there has widely been used a mercury thermometer, but recently a digital electronic clinical thermometer has also come into wide use.
Ordinary electronic clinical thermometers use a thermistor as a sensor and are provided with an arithmetic circuit for the calculation of temperature values and a digital display unit. But it takes two to three minutes for the measurement of temperature, which time is even longer than that required in mercury clinical thermometer. There is an electronic clinical thermometer of the type in which the final value is estimated from the progress of temperature rise during an initial one minute or so. But this type of an electronic clinical thermometer involves the problem that the so-estimated value is not always coincident with an actual value.
The problem of requiring time for the measurement of temperature is also related to the portion where the temperature is to be measured. It is the temperatures of such deep parts as head, chest and abdominal cavity that are maintained at predetermined values by the adjusting function of a living body. But it is difficult to directly measure the temperatures of those deep parts, so in general the temperature to be measured is rectal temperature, oral temperature, or axilla temperature. The axilla temperature measurement is widely adopted, but the axilla is usually in a somewhat open condition, so the skin temperature of that part is a little lower. When the axilla is closed with a clinical thermometer put therein, the skin temperature will begin rising and reach a certain temperature (equilibrium temperature) in 10 minutes or so. If at this point or thereafter the clinical thermometer is pulled out and checked, there will be obtained an accurate axilla temperature. But if the clinical thermometer is pulled out earlier, the temperature value shown thereon will be a little lower.
Another factor related to the temperature measurement time is the heat capacity of the sensor portion. In a mercury clinical thermometer, the temperature measurement goes through the process of warming the mercury bulb by the body temperature through the glass wall and reading the expansion of mercury, so the heat capacity of the object warmed is fairly large, requiring a measurement time of 2 to 3 minutes. Also in an electronic clinical thermometer, a metallic portion contacted with a part for measurement is warmed by the body temperature and the thermistor varies its resistance value depending on the temperature of the metallic portion, so the heat capacity of the object warmed (the metallic portion) is also large.
All of the above clinical thermometers are of a contact type, but there also are available non-contact type clinical thermometers, an example of which is the "non-contact type oral thermometer" disclosed in Japanese Patent Laid-Open No. 88627/83. In this oral thermometer, using a pyroelectric type infrared sensor, infrared rays from the oral cavity are condensed and input to the sensor after chopping, while the output of the sensor is amplified and calculation is made on the basis of a reference temperature signal to determine the body temperature, which is displayed on a display unit. Alternatively, using a thermistor as an infrared sensor, the oral thermometer is composed of a condensing system, the thermistor, an amplifier, an arithmetic unit, a display mechanism and a reference temperature detector.
As a method of measuring the body temperature by inserting a clinical thermometer into the ear cavity there have been proposed such methods as those disclosed in Japanese Patent Laid-Open Nos. 25427/85, 216232/85, 133331/85, 117422/86, 138130/86, and U.S. Pat. No. 3,282,106 (1966). However, these proposed methods have not been realized yet because of the following problems involved therein.
The Japanese patent laid-open 25427/85 is merely entitled "an ear-plug type body temperature sensor". It is uncertain whether the body temperature is measured by a contact heat transfer of a resistance bulb such as a thermistor or by using such a sensor as an Si sensor for detecting infrared rays (radiation). Thus, since it is uncertain what measuring means is used, it is actually impossible to constitute a clinical thermometer.
The patent laid-open 216232/85 discloses an ear-plug type thermometer which measures the body temperature by a contact heat transfer with the external auditory meatus, using a thermistor as a temperature sensor. However, since this method is a contact type, it can be easily estimated that a longer temperature measuring time is required than in an oral type electronic clinical thermometer.
The patent laid-open 133331/85 discloses an ear sealing type thermometer, which however is basically the same as the ear-plug type thermometer of the patent laid-open 216232/85 because it uses a thermistor and a transistor sensor as temperature sensors.
The patent laid-open 117422/86 discloses an ear insertion type thermometer using a thermopile as an infrared sensor. According to the method set forth therein, the sensor portion is maintained at a certain constant temperature and the body temperature is measured by a reference method, using a reference temperature source provided in the device. This method is technically superior, but a complicated construction is needed for maintaining the temperature of the sensor portion constant and for the provision of a reference temperature source, thus obstructing a low-cost production.
The patent laid-open 138130/86 discloses a method wherein infrared rays from the ear cavity are conducted to a pyroelectric sensor through an optical fiber. But an infrared optical fiber for the measurement of body temperature has not been developed yet. The wavelength band of the energy radiated from the body temperature is in the range of 8 to 13 .mu.m and there has not been developed a fiber capable of fully transmitting radiation of such wavelength band. At ordinary temperatures or thereabouts, such radiation from the fiber itself is not negligible, so from the standpoint of accuracy it is difficult to realize a clinical thermometer using an optical fiber. Even if such clinical thermometer were realized, it would be very expensive.
The U.S. Pat. No. 3,282,106 (1966) entitled "Method of Measuring Body Temperature" is concerned with a method of measuring the body temperature by detecting in a non-contact manner infrared radiation of 10 .mu.m in wave length emitted from a body cavity of a mammal typical of which cavity is the ear cavity. But this method is disadvantageous in that there occurs a temperature error because the change in temperature of the sensor portion is not considered.
Thus, the contact type clinical thermometers involve the problem that the time required for temperature measurement is long, and the conventional non-contact type clinical thermometers which are sensitive to infrared rays involve the problem of construction being complicated and the cost high.